Dissociation of the contributions of the prefrontal cortex and dorsomedial thalamic nucleus to spatially guided behavior in the rat.

Rats with lesions of the medial frontal cortex or dorsomedial nucleus of the thalamus (MD) were studied in two spatial localization tasks: the Morris water task and the 8-arm radial arm maze. Rats with medial frontal lesions failed to learn to swim from different locations to a hidden platform located at a specific place in a large tank (Morris task) and were impaired at learning the location of reward in the radial arm maze. Rats with MD lesions were not impaired at spatial orientation in either task. The results provide the first unequivocal evidence of a spatial orientation deficit following frontal lesions and lend support to the notion that the frontal cortex forms part of a 'spatial mapping system'. The results suggest that although MD is the major afferent to the frontal cortex, it does not provide necessary spatially-relevant input.